Anti-strip-out fastener

ABSTRACT

A fastener includes an axial shank and a clamping face extending radially from the shank. A plurality of serrations are formed on the clamping face and extend radially from a shank periphery to an outer periphery of the clamping face. The shank periphery is axially displaced away from the clamping face relative to the outer periphery of the clamping face to define a ramped surface.

FIELD OF THE INVENTION

The present invention relates to an anti-strip out fastener andassociated method.

BACKGROUND OF THE INVENTION

Fasteners for attaching two thin panels together often cause strip outwhen the torque required for drilling or tapping (“tapping torque”) thefasteners is statistically close to the torque cause stripping(“stripping torque”). At the same time, such fasteners must have goodgripping properties and avoid marring a finished panel surface whentapped into the panel. Current fastener designs attempt to balance theserequirements with various degrees of success; however fasteners withimproved anti-strip-out features are still desirable.

SUMMARY OF THE INVENTION

The present teaching provides for an anti-strip fastener. The fastenerincludes an axial shank and a clamping face extending radially from theshank. The fastener also includes a plurality of serrations connected tothe clamping face and extending radially from a shank periphery to anouter periphery of the clamping face. The serrations profile is suchthat improved gripping is provided without marring the surface beyondthe head diameter. The shank periphery is axially displaced away fromthe clamping face relative to the outer periphery of the clamping face.The fastener can also include a washer bounding the clamping surface.

The present teaching provides for a method of increasing anti-strip outresistance for a fastener having a head with a clamping surface having afirst boundary, and a shank extending from the head by providing aconvex or ramped configuration on the clamping surface with a pluralityof serrations. The serrations extend radially between the shank and thefirst boundary, such that the serrations define the convex surfacehaving an axial height that increases from the first boundary of theclamping face to the shank and is operable to provide anti-strip outresistance.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a fastener according to the presentteachings;

FIG. 2A is a bottom view of the fastener of FIG. 1;

FIG. 2B is a bottom view, showing a mirror image of the fastener of FIG.2A;

FIG. 3A is a sectional view of the fastener along axis 3A—3A of FIG. 2A;

FIG. 3B is a sectional view of the fastener along axis 3B—3B of FIG. 2B;

FIG. 4 is a side view of the fastener of FIG. 1;

FIG. 5 is a perspective view of an alternate embodiment of the fasteneraccording to the present teachings;

FIG. 6 is a side view of the fastener of FIG. 5; and

FIG. 7 is a bottom view of the fastener of FIG. 5.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The following description of various embodiments, including preferredembodiments, is merely exemplary in nature and is in no way intended tolimit the invention, its application, or uses.

Referring to FIGS. 1–4, a fastener 100 according to the presentteachings includes a shank 102, and a head 104 connected to the shank102 at one end of the shank 102. The shank 102 has an center axis “A”and can have a plurality of threads (schematically shown). The head 104includes a flange 106 having a clamping face 108. The clamping face 108comes in contact with and grips a panel surface (not shown) into whichthe fastener 100 is inserted for use.

The clamping face 108 can be bounded by a surface defining an annularwasher 110 that has an inner periphery 120, and an outer periphery 122,which coincides with the outer periphery of the flange 106. The washer110 can be substantially flat defining a plane 124. The clamping face108 includes a plurality of serrations 112, which extend generallyradially between the inner periphery 120 and the shank 102. Theserrations 112 outline a convex or ramped surface 116, which protrudesout of the plane 124 of the washer 110 and terminates at a periphery 118of the shank 102. When the washer 110 is omitted the clamping face 108extends to the outer periphery of the flange 106.

FIG. 2A illustrates an example of a fastener 100 having twelve forwardserrations 112; however, one skilled in the art will recognize that thenumber of serrations may be dictated by the specific application of thefastener. Each serration 112 protrudes outward from the clamping face108 and includes a root 130 embedded in the clamping face 108, and twoworking surfaces, which are a leading face 132 and a trailing face 136intersecting at a gripping edge 134. The plurality of gripping edges 134define the outline of the ramped surface 116. The height of theserration “h” in the direction of the axis A outward from the washersurface 124 and the clamping face 108, increases from the washer 110 tothe shank 102. As such, the ramped surface 116 defines an acute angle θrelative the washer surface 124 in the range of 10°–15° and preferablyat about 12.5°. However, one skilled in the art will recognize that theangle defined by the ramped surface may vary as dictated by the specificapplication of the fastener and the panel surface. When the fastener 100is tightened or tapped into a panel surface, the gripping edges 134enter the panel such that the ramped surface 116 becomes embedded intothe panel providing a strong grip. The washer 110 can reduce marring ofa surface finish of the panel surface.

The leading and trailing faces 132, 136 of the serrations 112 extendradially from the center axis A. The trailing face is oriented at anangle in the range of 10°–25°, and preferably at about 20° with respectto the plane of flange 106 to provide an oblique surface. An includedangle a is defined between the leading and trailing 132, 136 faces. Aspresently preferred, the included angle is about 90°. Thus, a leadingface 132 is slightly reclined relative to a direction of rotation fortightening the fastener. For example, the serrations 112 as shown in FIG3A engage in a clockwise (forward) direction for a right hand threadedfastener. It will be appreciated that a configuration which mirrors thatillustrated in FIG 3A could be provided for a left hand threadedfastener, as shown in FIGS. 2B and 3B. Since the structure of FIGS 2Band 3B is identical to that of FIGS 2A and 3A, with the exception ofserration orientation, similar reference numerals have been used.

FIGS. 5–7 illustrate a fastener 200 that is functional in a clockwisedirection or a counter clockwise direction according to the presentteachings. The fastener 200 includes a shank 202 and a head 204connected to the shank 202 at one end of the shank 202. The head 204includes a flange 206 having a clamping face 208. The clamping face 208comes in contact with and grips a panel surface (not shown) into whichthe fastener 200 is inserted.

The clamping face 208 can be bounded by a surface defining an annularwasher 210 that has an inner periphery 220, and an outer periphery 222,which coincides with the outer periphery of the flange 206. The washer210 is substantially flat defining a plane 224. The clamping face 208includes a plurality of serrations 212, which extend generally radiallybetween the inner periphery 220 and the shank 202. The serrations 212outline a ramped surface 216, which protrudes out of the washer plane224, outward from the clamping face 208, and terminates at a periphery218 of the shank 102. When the washer 210 is omitted the clamping face208 extends to the outer periphery of the flange 206.

FIG. 7 illustrates an example having eighteen serrations; however, oneskilled in the art will recognize that the number of serrations may bedictated by the specific application of the fastener. Each serration 212extends outward from the clamping face 208 and has a root 230 embeddedin the clamping face 208 and two working surfaces 232, 236 thatterminate at a gripping edge 234. The plurality of gripping edges 234define the outline of a convex or ramped surface 216. The height of theserration “h” in the direction of the axis A outward from the washersurface 224 and the clamping face 208, increases from the washer 210 tothe shank 202. As such, the ramped surface 216 defines an acute angle θrelative the washer surface 224 in the range of 10°–15° and preferablyat about 12.5°. However, one skilled in the art will recognize that theangle defined by the ramped surface may vary as dictated by the specificapplication of the fastener and the panel surface. When the fastener 200is tightened or tapped into a panel surface, the gripping edges 234enter the panel such that the ramped surface 216 becomes embedded intothe panel providing a strong grip. The washer 210 can reduce marring ofa surface finish of the panel surface.

The working surfaces 232, 236 of the serrations 212 extend radially fromthe center axis A. The working surfaces 232, 236 can extendsymmetrically from the gripping edges 234, creating a bi-directionaltoothed profile 238, such that the serrations 212 can engage in forward(clockwise) and reverse (counterclockwise) direction, as desired. Theworking surfaces 232, 236 define an included angle γ, which can be anacute angle. In the example shown in FIG. 7, the angle γ is illustratedas about 56°. The serrations 212 can be isolated, defining a gap 240between two consecutive serrations 212, or can alternately becontiguous. The number of serrations 212 can be chosen as desired for aparticular application. As used herein, the term gripping edge is usedbroadly to refer to a line of intersection between leading and trailingfaces as shown in FIGS. 1–4, as well as a relatively thin interveningsurface between leading and trailing faces as shown in FIGS. 5–7.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A fastener comprising: an axial shank having a free end; a clampingface extending radially from the shank; a washer bounding the clampingface defining a planar surface; and a plurality of serrations formed onthe clamping face and extending radially between the shank and thewasher, wherein each serration increases in axial height from the washerto the shank defining a ramped surface projecting towards the free endand having a first portion protruding above the planar surface and asecond portion extending below the planar surface.
 2. The fastener ofclaim 1, wherein the ramped surface is disposed at an angle in the rangeof 10–15° with respect to the clamping face.
 3. The fastener of claim 1,wherein each serration includes a leading face and a trailing facehaving said gripping edge disposed therebetween.
 4. The fastener ofclaim 3, wherein the trailing face defines an oblique surface withrespect to the washer.
 5. The fastener of claim 4, wherein each of thegripping edges is adapted to engage in a clockwise direction.
 6. Thefastener of claim 5, wherein an included angle between the leading faceand trailing face is about 90°.
 7. The fastener of claim 4, wherein eachof the gripping edges is adapted to engage in a counter clockwisedirection.
 8. The fastener of claim 7, wherein an included angle betweenthe leading face and trailing face is about 90°.
 9. The fastener ofclaim 4, wherein each of the gripping edges is adapted to engage in aselective clockwise and counterclockwise direction.
 10. The fastener ofclaim 9, wherein an included angle between the leading face and trailingface is about 90°.
 11. A fastener comprising: an axial shank having afree end; a clamping face extending radially from the shank; a washerbounding the clamping face defining a planar surface; and a plurality ofserrations formed on the clamping face and extending radially from ashank periphery, contacting an outer periphery of the clamping face,wherein the shank periphery is axially displaced away from the clampingface relative to the outer periphery of the clamping face, eachserration projecting toward the free end and having a first portionprotruding above the clamping face and a second portion extending belowthe clamping face.
 12. The fastener of claim 11, wherein the pluralityof serrations define a ramped surface extending from the outer peripheryof the clamping face to the shank periphery.
 13. The fastener of claim12, the ramped surface is disposed at an angle in the range of 10–15°with respect to the clamping face.
 14. The fastener of claim 13, whereineach serration includes a leading face and a trailing face having saidgripping edge disposed therebetween.
 15. The fastener of claim 14,wherein each of the gripping edges is adapted to engage in a clockwisedirection.
 16. The fastener of claim 14, wherein each of the grippingedges is adapted to engage in a counter clockwise direction.
 17. Thefastener of claim 14, wherein each of the gripping edges is adapted toengage selectively in clockwise and counter clockwise directions. 18.The fastener of claim 14, wherein the trailing face defines an obliquesurface with respect to the clamping face.
 19. The fastener of claim 18,wherein an included angle between the leading face and trailing face isabout 90°.